The basic lighting setup consists of a light source, a reflector and ballast (in case of MH and HPS).
Some additional bits and pieces might come in handy, however.
One group of such thing consists of all sort of devices that allows you to regulate the position of your reflector.
Usually, the reflector and a light source hangs from the ceiling or the box top and needs to be regularly adjusted so that it remains at the constant distant from the plants tops.
Too far, and your plants will grow more slowly then they could - too close, and instead of high quality marijuana, you will see your buds prematurely burned.
More advanced growers might also think about the automated mechanism that drives your light bulb around the plants, maximizing available light and consumed electricity.
Add on a E40 thread (if you are using HPS, MH or CFL), wiring and something to fix the whole thing together, and you're done.
And don't forget the spare parts - better be safe then sorry!